Composites are already known, a composite being an engineering material consisting of two or more combined materials which possesses properties as an engineering material not possessed by its individual components. Yet component properties as materials and component geometry do play a part in determining the properties of the composites. Size effects often play a particular part. The bond between the combined components is generally chemical or mechanical or a combination thereof.
Microstructured composite particles are also already known per se.
For example, European patent application EP 0 523 372 A1, by citing Japanese patent application JP62083029 A, discloses a process wherein a first material (referred to as “mother particles”) is surface coated with a second material which consists of smaller particles (referred to as “baby particles”). This is preferably accomplished using a surface-modifying device (“hybridizer”) which comprises a high-speed rotor, a stator and a sphere-shaped vessel, preferably comprising internal blades.
The mother and baby particles are mixed, preferably very finely divided and introduced into the hybridizer. There the mixture is preferably further very finely divided and preferably exposed repeatedly to mechanical forces, especially impact forces, compressive forces, frictional forces and shearing forces as well as the mutual interactions between the particles in order that the baby particles may become uniformly embedded in the mother particles.
Preferred rotor speeds are said to range from 50 m/s to 100 m/s, based on the circumferential velocity.
European patent application EP 0 523 372 A1 further describes fixing the composite particles by thermal spraying of a plasma, preferably by using a “reduced pressure plasma spraying device”, which preferably has an output level of not less than 30 kW.
This method yields a medical material comprising a substrate of a material having high strength and high biostability and a layer formed thereon which is obtainable by plasma spraying a substance exhibiting high bioaffinity. Preferred substances exhibiting high bioaffinity include hydroxylapatite, tricalcium phosphate, bioglasses and other substances having similar properties.
German patent application DE 42 44 254 A1 relates to a process for producing composite particles by securing to the surface of a thermoplastic material having an average particle diameter of 100 μm to 10 mm a substance which has a smaller particle diameter and a better thermal stability than the thermoplastic material, said process comprising the steps of:
first heating the substance which has the smaller particle diameter and the better thermal stability than the thermoplastic material to a temperature not less than the softening point of the thermoplastic material while stirring in an apparatus having a stirring mechanism and a heating means;
introducing the thermoplastic material into the apparatus; and
securing the substance having the better thermal stability to the surface of the thermoplastic material.
It is stated that as thermoplastic material (mother particles) of composite particles there can be used for example pellets or beads of various commercially available thermoplastic resins or plastics, e.g., ABS, AS, MBS, polyvinyl chloride, polyacetal, polyamide, polyethylene, polypropylene, polyethylene terephthalate, polystyrene, polycarbonate, polyacrylates. It is stated that the average particle diameter of the mother particles is preferably in the range from 100 μm to 10 mm.
Particularly suitable examples of the substance (baby particles) are stated to include in particular particles of inorganic material, such as silicate-containing particles (e.g., glass beads and the like), alumina particles and zirconia particles and particles of various metals which are excellent in heat resistance and abrasion resistance. The average particle diameter of the baby particles is stated to be smaller than that of the mother particles, preferably amounting to 1/10 or less of the average particle diameter of the mother particles, i.e., typically in the range from 1 μm to 1 mm.
European patent application EP 0 922 488 A2 concerns solid composite particles obtained by modifying the surface of a solid particle by securing fine particles to the surface of the particle which acts as a core and allowing a crystal or crystals of the fine particles to grow on a combination of the core and the fine particles in order to unalterably fix the fine particles on the core particle in a peel-resistant manner.
Suitable cores include inter alia cellulose derivatives, starch derivatives and also synthetic polymers, such as nylon, polyethylene and polystyrene.
Suitable fine particles include inter alia carbonates, phosphates and hydrogenphosphates, such as calcium monohydrogenphosphate.
U.S. Pat. No. 6,403,219 B1 discloses solid composite particles obtained by modifying the surface of a solid core particle by securing particles to the surface of the core particle in a non-peelable manner and allowing a crystal of a tied-down particulate component to grow in columnar or acicular fashion on the core particle, the tied-down particles being in a state of adhesive attachment to the surface of the core particle.
Suitable cores include inter alia cellulose derivatives, starch derivatives and also synthetic polymers, such as nylon, polyethylene and polystyrene.
Suitable fine particles include inter alia carbonates, phosphates and hydrogenphosphates, such as calcium monohydrogenphosphate.
The working example of this printed publication describes the preparation of composite particles from nylon 12 having an average particle diameter of 50 μm and tabular calcium monohydrogenphosphate having an average side length of about 50 μm, in a quantitative ratio of 10:1. The composite particles are obtained using a surface-modifying device (Nara Machinery Co. NHS-0). First a powder consisting of nylon 12 and calcium monohydrogenphosphate are treated with the surface-modifying device and the resulting product is then suspended in a suspension of calcium monohydrogenphosphate in order to allow the crystals to grow on the surface. The procedure of the U.S. Pat. No. 6,403,219 B1 patent is therefore associated with appreciable cost and inconvenience.
Japanese patent application JP 9239020 A describes an implant material for hard tissues which comprises composite particles wherein particles comprising a material having bioaffinity, for example hydroxylapatite or tricalcium phosphate, have a coating comprising a material of high hardness, for example zirconia or alumina.
Patent application US 2003/0124242 A1 concerns capsules having a mineral coating and a core comprising a polyhydroxylated compound.
The constituents of the mineral coating are stated to be alkaline earth metal carbonates or basic carbonates, basic transition metal carbonates, alkaline earth metal or transition metal sulfates, alkaline earth metal borates, alkaline earth metal halides and precipitated silica. Preferred alkaline earth metals are stated to include magnesium and calcium.
The polyhydroxylated compound is stated to include polysaccharides, such as threose, erythrose, arabinose, xylose, ribose, deoxyribose, rhamnose, fucose, glucosamine, galactosamine, N-acetylglucosamine, N-acetylgalactosamine, starch, amylopectin, amylose, araban, alginates, carrageenan, cellulose, chitosan, chondroitin sulfate, dextran, dextrin, fructosan, galactan, mannan, gum arabic, pectin, gum ghatti, galactoside, glycan, glycogen, hemicellulose, hyaluronic acid, inulin, lamarinarin, levan, mucoitin sulfate, nigeran, pentosan, polydextrose and xylan.
The examples of this printed publication describe the preparation of composite particles from guar having an average particle size of 32 μm and hydroxylapatite having an average particle size of 1.5 μm or from starch having an average particle size of 10 μm and calcium phosphate having an average particle size of 1 μm. The composite particles are each obtained using a surface-modifying device (Nara Machinery Co. NHS-0).
U.S. Pat. No. 5,011,862 describes hollow thermoplastic spheres, for example in PVC, PAN, polyalkyl methacrylate, PS, which include opacifiers such as TiO2, ZnO, CaCO3, talc, clay minerals or the like secured to or embedded in the surface thereof.
U.S. Pat. No. 4,915,884 discloses a granular material obtained by homogeneous mixing of a thermoplastic resin, such as PE for example, and of an adjuvant, such as calcium carbonate for example, subsequent extrusion of this mixture and comminution of the resulting strand of extrudate.
European patent application EP 2163 569 A1 concerns a process for producing resin particles from an acidic-group-containing thermoplastic resin or elastomer and a filler, for example calcium carbonate. The process produces resin particles by melting and mixing an acidic-group-containing thermoplastic resin or elastomer with filler particles and a water-soluble material in order to provide a resin composition comprising fine particles of resin which are formed by the thermoplastic resin and the filler particles. The resin composition is dispersed in a matrix including the water-soluble material. The matrix component is subsequently removed again from the resin composition in order to give the resin particles. The resulting resin particles each include a core particle, which includes the acidic-group-containing thermoplastic resin or elastomer, and filler particles immobilized on the outside surface of the core particle. This specific, extremely costly and inconvenient procedure of this printed publication leads to a porous structure on the part of the resin particles.
The printed publications Y. Shi, Y. Sun Fabrication and Characterization of a Novel Biporous Spherical Adsorbent for Protein Chromatography Chromatographia 2003, 57, pp. 29-35 and L. Wu, S. Bai and Y. Sun Development of Rigid Bidisperse Porous Microspheres for High-Speed Protein Chromatography Biotechnol. Prog. 2003, 19, pp. 1300-1306 describe the production of polymer beads by suspension polymerization of polyglycidyl methacrylate copolymers in the presence of superfine calcium carbonate. After polymerization, the calcium carbonate is leached out in order to obtain polymer beads having porous structures.
None of the aforementioned printed publications contemplates the use of precipitated calcium carbonate (PCC) particles or of resorbable polyesters as a constituent part of the composite particles described.
Again, the use of precipitated calcium carbonate in conjunction with molding compounds is already known in the literature, but again not as a constituent part of composite particles.
Thus, the publication T. D. Lam, T. V. Hoang, D. T. Quang, J. S. Kim Effect of nanosized and surface-modified precipitated calcium carbonate on properties of CaCO3/polypropylene nanocomposites Materials Science and Engineering A 501 (2009) 87-93 describes the effect of surface-modified calcium carbonate nanoparticles on the properties of CaCO3-polypropylene nanocomposites. However, the calcium carbonate particles therein are homogeneously dispersed in the polymer as a filler.
The publication L. Jiang, Y. C. Lam, K. C. Tam, D. T. Li, J. Zhang The influence of fatty acid coating on the rheological and mechanical properties of thermoplastic polyurethane (TPU)/nano-sized precipitated calcium carbonate (NPCC) composites Polymer Bulletin 57, 575-586 (2006) attends to the influence of fatty acid coatings on the rheological and mechanical properties of composites comprising thermoplastic polyurethane and precipitated calcium carbonate nanoparticles. Again, the calcium carbonate particles are homogeneously dispersed in the polymer as a filler.
The paper J. Cayer-Barrioz, L. Ferry, D. Frihi, K. Cavalier, R. Séguéla, G. Vigier Microstructure and Mechanical Behavior of Polyamide 66-Precipitated Calcium Carbonate Composites: Influence of the Particle Surface Treatment Journal of Applied Polymer Science, Vol. 100, 989-999 (2006) relates to the microstructure and the mechanical behavior of composites comprising polyamide 66 and precipitated calcium carbonate nanoparticles. Again, the calcium carbonate particles are homogeneously dispersed in the polymer as a filler.
Japanese patent application JP 41 39020 A describes the polymerization of polybasic carboxylic acids or polyfunctional isocyanates in a calcium carbonate composition comprising colloidal or particulate calcium carbonate. Again, the calcium carbonate particles are homogeneously dispersed in the polymer as a filler.
The publication M. Avella, S. Cosco, M. L. Di Lorenzo, E. Di Pace, M. E. Errico Influence of CaCO3 Nanoparticles Shape on Thermal and Crystallization Behavior of Isotactic Polypropylene based Nanocomposites Journal of Thermal Analysis and calorimetry, Vol. 80 (2005) 131-136 describes the influence of the shape of CaCO3 nanoparticles on the thermal and crystallization behavior of isotactic nanocomposites based on polypropylene. The calcium carbonate particles are homogeneously dispersed in the polymer as a filler.
The publication S. Weihe, M. Wehmöller, C. Schiller, C. Rasche, H. Eufinger, M. Epple Formgebung degradierbarer Werkstoffe mit Hilfe der Verfahrenskette zur Fertigung individueller CAD/CAM-Implantate Biomedizinische Technik/Biomedical Engineering, volume 46, number s1, pages 214-215 discloses an implant production by melt pressing of polyglycolide-co-lactide (PGLA), poly-L-lactide (PLLA) and graduated engineering materials consisting of multiple polymers and pressing by using a stainless steel mold.
Also described is a gas introduction process using poly-DL-lactide (PDLLA) and a Teflon mold. The process is based on CO2 being introduced under high pressure at room temperature. The CO2 is taken up by the polymer, lowering the glass transition temperature thereof. Pressure reduction causes the amorphous PDLLA to foam up and exactly fill out the mold. The process is stated to thereby enable the incorporation of thermolabile substances, for example antibiotics and osteoinductive proteins, and also to be employable for other amorphous polymers, for example PGLA.
One disadvantage of conventional polylactide implant materials is that they are invisible in an x-radiograph. Measurement of treatment progress by x-raying is accordingly impossible.